Various containers are used to package liquids, such as pressurized (e.g., carbonated) and unpressurized beverages. A commonly-used container is a polyethylene terephthalate (PET) bottle, which has been manufactured in various shapes and sizes. PET bottles are popular because they are inexpensive, lightweight, impervious to many gases and liquids and can be readily shaped into various designs and sizes. However, unlike containers formed of more rigid materials such as glass, PET containers can readily deform at low internal or external pressures, especially when the containers are thin-walled.
Certain PET containers or bottles have been designed with continuous ribs in order to provide some rigidity. However, although these ribs may perform satisfactorily when subject to moderate external pressures, they can readily deform when subjected to internal pressures, such as from the carbonation in certain beverages (50-100 psi). For example, certain containers for bottled water are provided with continuous ribs at the label panel area. Although the bottles are formed of relatively thin PET to lighten their weight, the continuous ribs add structural support at the area to be grasped by the consumer. That is, even though the containers are thin-walled, the pressure exerted by a consumer's grasping will not deform the containers because of the reinforcement provided by the continuous ribs. However, in some instances these water bottles are pressurized, such as by the addition of liquid nitrogen (up to about 40 psi), in order to survive distribution. It has been found, however, that this internal pressure tends to deform the continuous ribs over time. In some instances, the bottles would deform so as to “wash out” the continuous ribs. Improvements of this design have been attempted, such as by providing the continuous ribs with fillet radii. These modifications have achieved moderate success, but have not satisfactorily prevented deformation due to internal pressure.
Discontinuous ribs have also been proposed for plastic bottles for certain applications. U.S. Pat. No. 6,036,037 describes a plastic bottle that includes vacuum panels and reinforced bands above and below the vacuum panels. This particular bottle is for use in a “hot fill” application in which liquids are stored and sealed in the container while hot to provide adequate sterilization. The containers are typically filled under slight positive pressure and at temperatures approaching the boiling point of water when capped. However, cooling of the liquid product in the bottle usually creates negative internal pressure, which can partially collapse the bottle. Accordingly, the bottles are provided with six circumferentially spaced apart vacuum panels 3 in a central area to be covered by a label. When the volume of the hot product inside of the bottle shrinks during cooling, the faces of the vacuum panels are drawn inwardly to compensate for the reduction in pressure and prevent deformation of the other parts of the bottle. In addition, cylindrical bands 6 are disposed above and below the region of the vacuum panels 3. These bands 6 are formed of one or two circumferential hoop ribs 7, each made up of six recessed rib sections 8. These ribs provide hoop reinforcement to ensure completely cylindrical surfaces above and below the region of the vacuum panels, to which a label can be adhered. However, these circumferential hoop ribs are for compensating against negative internal pressure in conjunction with the vacuum panels and are not designed for providing against positive internal pressure.